Methods and systems for mobile device clock management

ABSTRACT

Disclosed are methods, systems and/or devices to calibrate a network time by acquisition of satellite positioning system (SPS) signals and different instances of time, and time-tagging SPS times according to the network time. In particular, the network time may be calibrated based, at least in part, on a first difference between first and second SPS times obtained at two SPS position fixes and a second difference between corresponding first and second time stamps.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Nos.61/899,791, entitled “Methods and Systems for Mobile Device ClockManagement,” filed Nov. 4, 2013, which is assigned to the assigneehereof and which is expressly incorporated herein by reference.

BACKGROUND

1. Field

Embodiments described herein are directed to application of mobiledevice clock management to permit efficient positioning operations.

2. Information:

The global positioning system (GPS) and other like satellite andterrestrial positioning systems have enabled navigation services formobile handsets in outdoor environments. Likewise, particular techniquesfor obtaining estimates of positions of mobile device in indoorenvironments may enable enhanced location based services in particularindoor venues such as residential, governmental or commercial venues.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive aspects are described with reference tothe following figures, wherein like reference numerals refer to likeparts throughout the various figures unless otherwise specified.

FIG. 1 illustrates a technique for calibrating a time tag uncertaintyusing two or more satellite positioning system (SPS) position fixesaccording to an embodiment.

FIG. 2 is a timing diagram illustrating a calibration of a local carriernetwork time using two or more SPS position fixes according to anembodiment.

FIG. 3 is a flow diagram of a process to calibrate a local network timeaccording to an embodiment.

FIG. 4 is a schematic diagram of a system for crowdsourcing messages forcreating or updating positioning assistance data according to anembodiment.

FIG. 5 is a flow diagram of a process to track an uncertainty of a clockmaintained at a base station according to an embodiment.

FIG. 6 is a timing diagram illustrating a technique to calibrate a sleepclock of a mobile device according to an embodiment.

FIG. 7 is a flow diagram of a process for updating a sleep clock timeaccording to an embodiment.

FIG. 8 is a schematic block diagram illustrating aspects of an exemplarydevice, in accordance with an implementation.

FIG. 9 is a schematic block diagram of an example computing platform inaccordance with an implementation.

SUMMARY

Briefly, particular implementations are directed to a method, at amobile device, comprising: obtaining a first value of a sleep counterand a first time stamp in response to the mobile device entering a lowerpower state, wherein the first time stamp is referenced to a localnetwork time; entering a higher power state to acquire a paging signal;obtaining a second value of the sleep counter and a second time stampwhile in the higher power state, wherein the second time stamp isreferenced to the local network time; returning to the lower powerstate; and estimating an increment cycle of the sleep counter based, atleast in part, on a first difference between the first time stamp andthe second time stamp, and second difference between the first value ofthe sleep counter and the second value of the sleep counter.

Another particular implementation is directed to a mobile devicecomprising: a receiver; a sleep counter circuit; and one or moreprocessors configured to: obtain a first value of a sleep counter and afirst time stamp in response to the mobile device entering a lower powerstate, wherein the first time stamp is referenced to a local networktime; transition the mobile device to a higher power state to acquire apaging signal received at the receiver; obtain a second value of thesleep counter and a second time stamp while in the higher power state,wherein the second time stamp is referenced to the local network time;transition the mobile device to the lower power state; and estimate anincrement cycle of the sleep counter based, at least in part, on a firstdifference between the first time stamp and the second time stamp, andsecond difference between the first value of the sleep counter and thesecond value of the sleep counter.

Another particular implementation is directed to a non-transitorystorage medium comprising machine-readable instructions stored thereonwhich are executable by one or more processors of a mobile device to:obtain a first value of a sleep counter and a first time stamp inresponse to the mobile device entering a lower power state, wherein thefirst time stamp is referenced to a local network time; transition themobile device to a higher power state to acquire a paging signal; obtaina second value of the sleep counter and a second time stamp while in thehigher power state, wherein the second time stamp is referenced to thelocal network time; transition the mobile device to the lower powerstate; and estimate an increment cycle of the sleep counter based, atleast in part, on a first difference between the first time stamp andthe second time stamp, and second difference between the first value ofthe sleep counter and the second value of the sleep counter.

Another particular implementation is directed to an apparatus at amobile device comprising: means for obtaining a first value of a sleepcounter and a first time stamp in response to the mobile device enteringa lower power state, wherein the first time stamp is referenced to alocal network time; means for entering a higher power state to acquire apaging signal; means for obtaining a second value of the sleep counterand a second time stamp while in the higher power state, wherein thesecond time stamp is referenced to the local network time; means forreturning to the lower power state; and means for estimating anincrement cycle of the sleep counter based, at least in part, on a firstdifference between the first time stamp and the second time stamp, andsecond difference between the first value of the sleep counter and thesecond value of the sleep counter.

It should be understood that the aforementioned implementations aremerely example implementations, and that claimed subject matter is notnecessarily limited to any particular aspect of these exampleimplementations.

DETAILED DESCRIPTION

The global positioning system (GPS) and other like satellite positioningsystems (SPSs) have enabled navigation services for mobile handsets inoutdoor environments. To obtain a location or position fix (or locationestimate), an SPS receiver may acquire SPS signals from four or more SPStransmitters (e.g., on space vehicles). With detection of timingparameters in the acquired SPS signals, the SPS receiver may obtaincorresponding pseudorange measurements to the SPS transmitters. Withknowledge of locations of the SPS transmitters (e.g., from an almanac)and the pseudorange measurements, the SPS receiver may compute aposition fix.

To efficiently acquire an SPS signal for obtaining a pseudorangemeasurement, an SPS receiver may define a two-dimensional search windowcomprising Doppler dimension and a time dimension. The time dimensionmay be defined, at least in part, by an uncertainty in SPS time anduncertainty in a location of the SPS receiver. Here, reducinguncertainty in SPS time and/or uncertainty in location may permit areduction in the dimension of the two-dimensional search window. Thismay be particularly useful in achieving low-power operation orconserving battery life by shortening a process for searching/acquiringSPS signals within a predefined search window.

According to an embodiment, a mobile device may determine a window forsearching for an SPS signal based, at least in part, on a local carriernetwork time. Here, if the local carrier network time is accuratelyreferenced to SPS time, an uncertainty in SPS time may be very small.For example, before a mobile device generates a position fix, the timeuncertain maintained at the mobile device may be about 30.0 μsec for aCDMA network, for example, and as high as 2.0 seconds for a UMTSnetwork, for example. A particular uncertainty maintained at the mobiledevice may then be used for determining a search window for acquiringSPS signals for computing a position fix. Having generated the positionfix, the mobile device may have a time uncertainty of on the order of afew nanoseconds (e.g., 10.0 nanoseconds). On the other hand, if thenetwork carrier time is not accurately referenced to SPS time, anuncertainty in SPS time may be larger.

According to an embodiment, an SPS receiver of a mobile device maycalibrate a local carrier network time to SPS time by time-tagging twoor more SPS position fixes. Here, in a particular implementation, an SPSreceiver may obtain an accurate measurement or indication of SPS time inthe course of obtaining an SPS position fix (e.g., by detecting a bitedge of a data signal modulating an acquired SPS signal). According toan embodiment, an SPS receiver may associate two or more SPS timescorresponding to SPS position fixes with time tags according to a localcarrier network time. As discussed below in connection with FIGS. 1 and2 below with a particular non-limiting example, defining multipleexpressions or constraints with the SPS times which are time-taggedaccording to a local network time, an SPS receiver may reduceuncertainty in an expression of SPS time as a function of the localcarrier network time.

According to an embodiment, a mobile device may employ a local carriernetwork time based on a base station clock to estimate an SPS time.While an air interface standard may specify an allowable base stationclock drift rate from an SPS time reference of, for example, under 50ppb (50 ns/s), a base station in the field may in fact have betterperformance (e.g., clock drift rate of under 10 ppb) (3 gpp: GSM:Wide-Area 50 ppb, Pico-Cell 100 ppb (45.010)); UMTS: Wide-Area 50 ppb,Pico-Cell 100 ppb, Femto-Cell 250 ppb (FDD 25.104, TDD 25.105); LTE:Wide-Area 50 ppb, Pico-Cell 100 ppb, Femto-Cell 250 ppb (36.104, sec6.5.1); TD-SCDMA: Wide-Area 50 ppb (from YD/T 1719-2007 Chinese TD-SCDMARAN equipment spec, Sec 17.3, NodeB synchronization requirements). In aparticular implementation, a mobile device may reduce an uncertainty incalibrating a base station clock relative to SPS time in the mobiledevice, and then use a calibrated growth rate to increase over time anuncertainty in local carrier network time. As pointed out above, such areduced clock uncertainty may enable a shorter time-to-fix and/or lowerpower consumption.

In another implementation, measurements of network time from multiplemobile devices/SPS receivers may be crowdsourced in a network cloud foruse as assistance data. Here, a mobile device may download parametersfrom a database server or cloud, so as to reduce or eliminatecalibration. In another implementation, uncertainty in a local carriernetwork time may be reduced if it is known whether the mobile device isstationary, or moving at pedestrian speed.

In a particular implementation, a time of arrival of a cellular downlinksignal may be used for determining a time tag or time stamp value. Here,a time of arrival may vary as the mobile device travels closer to orfurther away from a base station transmitting the cellular downlinksignal. In a particular case in which a mobile device has a sensorresponsive to motion (e.g., accelerometer), an uncertainty in a time tagneed not include an uncertainty arising from possible movement (e.g., a10 km uncertainty in range to the base station may translate to a 30.0μs uncertainty in time). In another particular implementation, anuncertainty in a time of a time tag or time stamp may be used tocalibrate a mobile device sleep clock in a paging cycle. This may make atime uncertainty small if an SPS position fix request occurs while acellular modem is in a sleep state.

According to an embodiment, an uncertainty in a measured SPS time maycomprise an uncertainty in a time tag or time stamp value (e.g., timetag according to a local network time) in combination with (e.g., addedto) a time uncertainty arising from an uncertainty in propagation time.A mobile device may obtain a time reference to a local carrier networkclock by acquiring a signal transmitted by a base station. As discussedbelow in a particular example, an uncertainty in propagation time mayarise from a change in a distance between a transmitting base stationand a receiving mobile device, which affects the time arrival of thesignal at the receiving mobile device. A change in a propagation delaymay be measured based on a measurement of change in a distance betweenthe transmitting base station and the receiving mobile device. This maybe measured using any one of several techniques such as, for example,well known trilateration techniques, tracing a trajectory of movement ofthe mobile device using well known position techniques, measurementsobtained from inertial sensors (e.g., magnetometer, accelerometer,gyroscope, etc.) applied to a dead-reckoning procedure, just to providea few examples. Determining a change in propagation delay based on ameasured change in a distance between the transmitting base station andthe receiving mobile station may enable a reduction in a timeuncertainty or acquisition window for acquisition of SPS signals.

FIG. 1 illustrates a technique for calibrating a time tag or time stampuncertainty using two or more SPS position fixes according to anembodiment. Here, a mobile device 102 may travel between two differentlocations relative to a base station. In this particular scenario,mobile device 102 obtains two different SPS position fixes at twodifferent locations at SPS times (e.g., GPS times) T1 and T2, withuncertainties ΔT/and ΔT2, respectively. Locations 104 and 106 areseparated by a distance D, with uncertainty ΔD. Mobile device 102 mayassociate network time tags or time stamps NT1 (e.g., signal frameedge1) and NT2 (e.g., signal frame edge2) to corresponding SPS times T1and T2, with uncertainties ΔNT1 and ΔNT2, respectively. In theparticular illustrated embodiment, time tags or time stamps NT1 and NT2are reference to a network time maintained at, and a signal transmittedby, a single base station (e.g., base station 100).

In a particular example scenario, ranges D1 and D2 from a base stationto the mobile device at first and second locations 104 and 106 may beunknown. An SPS time BNT1 at an instance that signal edge1 istransmitted from the base station may be set forth in expression (1) asfollows:

BNT1=(T1+ΔT1)+ΔNT1−D1/c  (1)

where c is the speed of light.

Similarly, an SPS time BNT2 at an instance that a signal edge2 istransmitted from the base station may be set forth in expression (2) asfollows:

BNT2=(T2+ΔT2)+ΔNT2−D2/c.  (2)

A difference in SPS times obtained at the first and second positionfixes may thus be set forth in expression (3) as follows

BNT12=(T2−T1)+ΔT1+ΔT2+ΔNT1+ΔNT2−(D2−D1)/c.  (3)

FIG. 2 is a timing diagram showing timelines for SPS time, local networktime as maintained at a mobile device (e.g., mobile device 102) andlocal network time as maintained at a base station (e.g., base station100). Here, a base station timing error during NT1 to NT2 may be setforth in expression (4) as follows:

Terr=BNT12−(NT2−NT1).  (4)

According to an embodiment, if D is small or negligible a base stationclock drift rate of a local network time (e.g., as maintained by a clockat mobile device or base station) may be set forth in expression (5) asfollows:

$\begin{matrix}\begin{matrix}{{Trate} = {{Terr}/\left( {{{NT}\; 2} - {{NT}\; 1}} \right)}} \\{= {\begin{bmatrix}{\left( {{T\; 2} - {T\; 1}} \right) + {\Delta \; T\; 1} + {\Delta \; T\; 2} + {\Delta \; {NT}\; 1} +} \\{{\Delta \; {NT}\; 2} - {D/c} - \left( {{{NT}\; 2} - {{NT}\; 1}} \right)}\end{bmatrix}/{\left( {{{NT}\; 2} - {{NT}\; 1}} \right).}}}\end{matrix} & (5)\end{matrix}$

In one particular application, clock uncertainty values at SPS fixesΔT/and ΔT2 may be a few ns while time tag or time stamp uncertaintyvalues ΔNT1 and ΔNT2 may be ˜1.0 μs (e.g., the time uncertainty of timetag or time stamp operation itself). In a particular application, tomake the time tag or time stamp uncertainty much smaller than 50 ppbduring calibration of network time, a constraint(ΔNT1+ΔNT2)/(NT2−NT1)<5.0 ppb may be maintained. If ΔNT1+ΔNT2=2.0 μs,for example, (NT2−NT1)>2.0 μs/5 ppb=400 s. If the time tag or time stampoperation uncertainty is smaller, the time required may be shorter. Adistance D between two positions may also impact an uncertainty of thecalibration. If D is close to 0.0, there may be no impact onuncertainty.

FIG. 3 is a flow diagram of a process to calibrate a local network timemaintained at a base station according to an embodiment. At block 152 areceiver (e.g., at mobile device 102) may acquire one or more first SPSsignals to obtain a first position fix including a first SPS time (e.g.,by detecting a bit edge in a data signal modulating one or more acquiredSPS signals). As pointed out above, the receiver may comprise a clock tolocally maintain a local network time (e.g., at a local carriernetwork). Responsive to the position fix obtained at block 152, thereceiver may obtain a first time tag or time stamp referenced to thelocal network time (e.g., a local network time at a base station such asbase station 100).

Subsequent to obtaining the position fix at block 152, the receiver maymove its location from a first location to a second location (e.g., adistance D from location 104 to location 106). At block 156, thereceiver may acquire one or more second SPS signals to obtain a positionfix including a second SPS time. In particular implementation, first andsecond SPS signals acquired at blocks 152 and 156 may be transmitted bydifferent SPS transmitters that are in the same global network satellitesystem (GNSS) such that they are synchronized (e.g., to a common timereference). However, first and second SPS signals acquired at blocks 152and 156 may alternatively be transmitted from two different GNSSs if theGNSSs are synchronized to one another. At block 158, the receiver mayobtain a second time stamp responsive to the second position fix which,like the first time stamp obtained at block 154, is referenced to thelocal network time.

At block 160, a time uncertainty (e.g., an uncertainty in network timerelative to an SPS time) may be determined based, at least in part, on afirst difference between the first and second SPS times obtained atblocks 154 and 158, and a second difference between the first and secondtime stamps obtained at blocks 154 and 158. For example, block 160 maycompute a time uncertainty according to expression (6) discussed below.Accordingly, in a particular implementation, block 160 may compute Terrand/or Trate discussed above according to expressions (4) and (5).Values for D, D1 and D2 may be computed as Euclidean distances based, atleast in part, on a known location of a base station transmitter andlocations from position fixes obtained at blocks 152 and 156. It shouldbe understood, however, that these are merely examples of how a localnetwork time may be calibrated at a receiver and claimed subject matteris not limited in this respect.

As described above, a mobile device may measure a clock error (e.g.,Terr) and/or drift rate (e.g., Trate) associated with a clock maintainedat a particular base station against SPS times obtained at SPS positionfixes taken at two different times (and possibly different locations).In a particular implementation, the mobile device may store such a clockerror and/or drift rate measured for this particular base station.Optionally, the mobile device may store a clock error and/or draft ratefor any base station that the mobile device is in communication withwhile performing at least two SPS position fixes as discussed above. Themobile device may use the measured drift rate to determine an estimatedclock error at a particular instance. In one example, the mobile devicemay perform a position fix and then turn off its SPS receiver but keeptrack of time via a base station signal (e.g., pilot etc.)). Before themobile device makes a subsequent position fix (e.g., at block 156), alocal network time may be propagated at the mobile device using the basestation signal (time tagging) so that the error may be predicted basedon the measured base station drift and/or drift rate (from memory aspreviously measured or downloaded from a server). For example, adistance between the mobile device (e.g., mobile device 102) and a basestation (e.g., base station 100) may increase as the mobile device movesfrom a first location (e.g., location 104) to a second location (e.g.,location 106). Referencing network time to SPS time at a first positionfix at block 152, network time may be used for determining anacquisition window for acquiring one or more SPS signals at block 156.Network time at the second location in advance of acquiring signals atblock 156 may be propagated based, at least in part, on (D2−D1)/c. WhileD1 may be accurately known from an SPS position fix at block 152, D2 maybe estimated/measured using other techniques. For example, as discussedabove, D2 or D2−D1 may be measured using any one of several techniquessuch as, for example, well known trilateration techniques, tracing atrajectory of movement of the mobile device using well known positiontechniques, measurements obtained from inertial sensors (e.g.,magnetometer, accelerometer, gyroscope, etc.) applied to adead-reckoning procedure, just to provide a few examples. It should beunderstood, however, that this is merely an example of how a change inpropagation delay may be computed and that claimed subject matter is notlimited in this respect.

In an example implementation, a time uncertainty may be computed for afuture time according to expression (6) has follows:

T _(unc)(t ₂)=T _(unc)(t ₁)+Trate·(t ₂ −t ₁)  (6)

where:

T_(unc) (t₁) is an uncertainty in time at time t₁; and

T_(unc) (t₂) is an uncertainty in time at time t_(2.)

In a particular example, a position fix made by a mobile device at timet₁ may provide T_(unc) (t₁)=15.0 nsec. Assuming a measured Trate of 10ppb or 10.0 nsec/sec as the mobile device goes to sleep, if the mobiledevice awakens to obtain an SPS position fix three hours later themobile device may compute T_(unc) (t₂)=15.0 nsec+10.0 nsec/sec (3*3600sec)=108 μsec. Using a default drift rate of 50 ppb instead of themeasured drift rate Trate which instead provide T_(unc) (t₂)=540 μsec.This technique of computing T_(unc) (t₂) according to expression (6)from a measured drift rate Trate instead of a default drift rate mayenable improved performance over techniques that assume a worst casedrift specified in a particular air interface standard for base stationperformance (while in fact a base station clock may be more stable thana worst case allowable by an applicable air interface standard).

As pointed out above, detection of a frame boundary delay on a signaltransmitted by a base station may depend on a distance from a basestation (as there is a signal flight time from the base station to themobile device). Accordingly, to accurately measure drift, it may beuseful to determine whether a mobile device has not moved significantly.For example, output signals from devices such as accelerometers,gyroscopes, motion sensors, magnetometers, or other devices that maysense a change in position, orientation, etc. Additionally, detection ofthe same short range signals such as Bluetooth or WiFi may indicate anabsence of movement.

It is also pointed out that a femtocell or WiFi access point may alsomaintain a more stable clock than that of a mobile device. As such, thetechniques described herein may be applicable to not only base stationsbut also a variety of other stationary wireless transceivers. Since aclock error may be smaller than a maximum allowable drift according to aparticular air interface standard, a search window for acquiring an SPSsignal may be reduced significantly (perhaps 2-5×; which may depend onhow long it has been since the last fix if assuming a constant drift).

According to an embodiment, a measured base station clock drift may bestored locally in a mobile device base station almanac (e.g., as asubset of an entire base station almanac based, at least in part, onwhere the mobile device is/has been) and/or periodically (orimmediately) uploaded to location server that maintains an overall basestation almanac. Alternatively, a base station identifier (e.g., BTS IDinformation such as SID/NID/BSID or MACID) may be updated depending on aparticular type of base station it was. A crowd-sourcing server maycombine uploaded measurements to compute parameters such as mean,median, statistical fit, etc., and make an appropriate indication ofbase station clock drift (e.g., Terr) and/or drift rate (e.g., Trate)available to mobile devices as positioning assistance data.

FIG. 4 is a system diagram of a system for crowdsourcing messages forcreating or updating positioning assistance data according to anembodiment. Mobile devices 212 and 216 may be in communication with acarrier network through network cloud 208. Mobile devices 112 may obtainmeasurements based on observations of signals transmitted from basestations 213 and SPS transmitters 210, and forwarded these measurementsin messages to crowdsourcing server 202. Crowdsourcing server 202 maycompute positioning assistance data to be forwarded to location server206. Mobile devices 216 may then receive positioning assistance datafrom messages transmitted by location server 206 through network cloud208.

As discussed above in particular embodiments, a mobile device 212 mayacquire SPS signals transmitted by SPS transmitters 210 to obtain two ormore SPS position fixes providing corresponding SPS times. Being incommunication with a base station 214, the mobile device 212 may obtaina local network time being maintained by the base station 214 and maytime-tag the two or more position fixes according to the local networktime. In a particular implementation, as discussed above, for theparticular base station 214, the mobile device 212 may compute Terrand/or Trate according to expressions (4) and (5), and forward thesevalues in messages to crowdsourcing server 202. For the particular basestation 214, crowdsourcing server may aggregate values of Terr and/orTrate from multiple mobile devices 212 to provide positioning assistancedata (e.g., aggregated, filtered and/or averaged values for Terr and/orTrate) available to mobile devices 216.

FIG. 5 is a flow diagram of a process to track an uncertainty of a clockmaintained at a base station according to an embodiment. At block 302, adatabase may be maintained to track an uncertainty of a clock maintainedat a base station. For example, such a database may be maintained atcrowdsourcing server 202. At block 304, a calibration result may bereceived from a mobile device (e.g., a mobile device 212) an uncertaintyin a clock maintained at the at least one base station (e.g., a computedvalue for Terr and/or Trate). At block 306, the uncertainty tracked in adatabase at block 306 may be selectively updated based, at least inpart, on whether an uncertainty level indicated by the calibrationresult is less than a threshold value. Updating the tracked uncertaintywith a calibration result having an uncertainty exceeding the thresholdvalue, for example, may not improve the usefulness of the tracked clockuncertainty.

According to an embodiment, a mobile device may be maintained in a lowpower state during which, for example, certain functions are powereddown. For example, a mobile phone may be maintained in a sleep statethat is interrupted periodically with short periods in which a receivermay acquire a signal (e.g., a paging slot to acquire a paging signalfrom a cellular transmitter). In one particular implementation, forexample, on five second periods a mobile phone may briefly awaken for a90-100 msec duration to acquire paging signal. While the mobile deviceis in a lower power state such as a sleep state, the mobile device maymaintain a sleep counter to be used in propagating time maintained by asystem clock. As pointed out above, having an accurate system clock timemay enable the mobile device to obtain estimates of its location byacquiring SPS signals with a small search window, enabling a fasttime-to-fix.

In a particular implementation, a mobile device in a sleep state orlower power state may operate such that power may be removed from awireless transceiver (e.g., WWAN or cellular transceiver) and/or othercomponents. In such a lower power state, a wireless transceiver may nothave full functionality to receive signals from and transmit signals toa wireless network, but functionality may be quickly restored by fullypowering the device. While a wireless transceiver may have a reducedfunctionality in such a lower power state, in an embodiment a mobiledevice may have an SPS receiver that is powered to acquiring signalswhile the mobile device is in the lower power state. As such, during asleep or lower power state a process on the mobile device may be capableof issuing a request to perform an SPS position fix and an SPS receivermay be capable of fulfilling this request even if the mobile device isin the lower power state. Having an accurate system clock time availableas the SPS receiver receives a request while the mobile device is in thelower power state may enable the small search window and correspondingfast time-to-fix.

According to an embodiment, a system clock value of a mobile device maybe propagated while the mobile device is in a sleep state according toexpression (6) as follows:

T _(C2) =T _(C1) +ΔT  (6)

Where:

-   -   T_(C1) is a beginning system clock time (e.g., at a time where a        mobile device enters lower power state such as a sleep state);    -   T_(c2) is a propagated system clock time; and

ΔT is an amount that a system time is propagated.

According to an embodiment, an amount of time that a system clock ispropagated ΔT may be computed based, at least in part, a change in avalue of a counter that is incremented on increment cycles from a starttime (e.g., entering a sleep state) and an end time (e.g., servicing arequest for an SPS position fix) according to expression (7) as follows:

ΔT=(C2−C1)T _(SC),  (7)

where:

-   -   T_(SC) is an increment cycle of a sleep counter;    -   C1 is a value of a sleep counter at an instance that a mobile        device enters a sleep state; and

C2 is a value of a sleep counter at an end time.

According an embodiment, a duration of an increment cycle of a sleepcounter T_(SC) may be estimated based, at least in part, on a localnetwork time maintained at a base station as described above. Forexample, as illustrated in FIG. 6, values of a sleep clock time may betime-tagged or time stamped at two different instances according to alocal network time. Here, for example, values of a sleep counter(C_(ST1) and C_(ST2)) may be time-tagged or time stamped with a networktime at network times NT1 and NT2. A value for T_(SC) may be computedaccording to expression (8) as follows:

T _(SC)=(NT2−NT1)/(C _(ST2) −C _(ST1))  (8)

In a particular implementation, network times for time tags NT1 and NT2may be obtained from acquisition of paging signals at paging slots.According to an embodiment, uncertainties in time tags NT1 and NT2, anduncertainties in sleep clock counts (e.g., to account for fractions ofcount increments) may contribute to uncertainties in an estimate ofT_(SC) computed according to expression (8). For example,contemporaneously with performing a time tag, a sleep count may be readto achieve an uncertainty to within 4.0 μs. An additional 1.0 μs may beincluded to increase a total uncertainty to 5.0 μs. Suppose, forexample, that time tags NT1 and NT2 are spaced by 1.28 sec and a sleepclock may be calibrated to an accuracy of 10.0 μs/1.28 sec=7.8 ppm(distance moved by mobile device in 1.28 sec may be small and ignored).In a particular implementation, if an SPS session is started during anLTE sleep state, there may be no sleep time tag needed. Instead, a sleepcounter may be read again. A time uncertainty may be obtained by using alast regular time tag uncertainty, plus the sleep clock uncertainty part(e.g., 10.0 μs/1.28 s× time since last regular time tag), plusuncertainty from temperature introduced into sleep clock drift.

As shown in FIG. 7, for example, a mobile device may obtain a firstvalue of a sleep counter in response to the mobile device entering alower power state (e.g., a sleep state) at block 502. The mobile devicemay then enter a higher power state to acquire a paging signal at block504. Block 504 may occur, for example, as the mobile device awakens froma sleep state and resumes to a higher power state during a paging slot.Acquiring the paging signal, the mobile device may sample the localnetwork time again. Block 406 may then obtain a second value of thesleep counter and a second time stamp while the mobile device is in thehigher power state. The second time stamp is referenced to the localnetwork time and may be based, at least in part, on the local networktime as sampled from acquisition of the paging signal. At block 508, themobile device may return to a lower power state. In a particularimplementation, the first and second values of the sleep counterobtained at blocks 502 and 506 may comprise C_(ST1) and C_(ST2),respectively. In a particular implementation, the first and second timestamps may be referenced to a local network time (e.g., as network timesNT1 and NT2). At block 510, a mobile device may estimate an incrementcycle of the sleep counter (e.g., T_(SC)) according to expression (8)above, for example. The estimate of the increment cycle may then be usedto update a system clock time to define a time uncertainty for obtainingan SPS position fix as discussed above.

FIG. 8 is a schematic diagram of a mobile device that may be used forobtaining SPS position fixes and/or calibrating local carrier networktime based on two or more SPS position fixes that are time taggedaccording to local carrier network time according to an embodiment. Incertain embodiments, mobile device 1100 may also comprise a wirelesstransceiver 1121 which is capable of transmitting and receiving wirelesssignals 1123 via wireless antenna 1122 over a wireless communicationnetwork. Wireless transceiver 1121 may be connected to bus 1101 by awireless transceiver bus interface 1120. Wireless transceiver businterface 1120 may, in some embodiments be at least partially integratedwith wireless transceiver 1121. Some embodiments may include multiplewireless transceivers 1121 and wireless antennas 1122 to enabletransmitting and/or receiving signals according to correspondingmultiple wireless communication standards such as, for example, versionsof IEEE Std. 802.11, CDMA, WCDMA, LTE, UMTS, GSM, AMPS, Zigbee andBluetooth, just to name a few examples.

Mobile device 1100 may also comprise SPS receiver 1155 capable ofreceiving and acquiring SPS signals 1159 via SPS antenna 1158. SPSreceiver 1155 may also process, in whole or in part, acquired SPSsignals 1159 for estimating a location of mobile device 1000. Forexample, SPS receiver 1155 may be capable of acquiring SPS signals toobtain a first position fix including a first SPS time at block 152 andto obtain a second position fix including a second SPS time at block156. In some embodiments, general-purpose processor(s) 1111, memory1140, DSP(s) 1112 and/or specialized processors (not shown) may also beutilized to process acquired SPS signals, in whole or in part, and/orcalculate an estimated location of mobile device 1100, in conjunctionwith SPS receiver 1155. Storage of SPS or other signals (e.g., signalsacquired from wireless transceiver 1121) for use in performingpositioning operations may be performed in memory 1140 or registers (notshown). As such, general-purpose processor(s) 1111, memory 1140, DSP(s)1112 and/or specialized processors may provide a positioning engine foruse in processing measurements to estimate a location of mobile device1100.

Also shown in FIG. 8, mobile device 1100 may comprise digital signalprocessor(s) (DSP(s)) 1112 connected to the bus 1101 by a bus interface1110, general-purpose processor(s) 1111 connected to the bus 1101 by abus interface 1110 and memory 1140. Bus interface 1110 may be integratedwith the DSP(s) 1112, general-purpose processor(s) 1111 and memory 1140.In various embodiments, functions may be performed in response executionof one or more machine-readable instructions stored in memory 1140 suchas on a computer-readable storage medium, such as RAM, ROM, FLASH, ordisc drive, just to name a few example. The one or more instructions maybe executable by general-purpose processor(s) 1111, specializedprocessors, or DSP(s) 1112. Memory 1140 may comprise a non-transitoryprocessor-readable memory and/or a computer-readable memory that storessoftware code (programming code, instructions, etc.) that are executableby processor(s) 1111 and/or DSP(s) 1112 to perform functions describedherein.

In a particular implementation, general-purpose processor(s) 1111 and/orDSP(s) 1112 in combination with machine-readable instructions stored onmemory 1140 may execute all or portions of actions and/or operations setforth in blocks 152 through 160 shown in FIG. 3. For example, based, atleast in part, on acquisition of a signal transmitted by a base stationand acquired at wireless transceiver 1121, general-purpose processor(s)1111 and/or DSP(s) 1112 in combination with machine-readableinstructions stored on memory 1140 may obtain time stamps referenced toa network time at blocks 154 and 158. General-purpose processor(s) 1111and/or DSP(s) 1112 in combination with machine-readable instructionsstored on memory 1140 may then determine a time uncertainty at block160.

In another particular implementation, general-purpose processor(s) 1111and/or DSP(s) 1112 in combination with machine-readable instructionsstored on memory 1140 may execute all or portions of actions and/oroperations set forth in blocks 502 through 510 shown in FIG. 7. Atblocks 502 and 504, for example, general-purpose processor(s) 1111and/or DSP(s) 1112 in combination with machine-readable instructionsstored on memory 1140 may obtain first and second values of a sleepcounter maintained at sleep counter circuit 1142. At blocks 506 and 508,general-purpose processor(s) 1111 and/or DSP(s) 1112 in combination withmachine-readable instructions stored on memory 1140 may further applyfirst and second time stamps to respective first and second values ofthe sleep counter. Finally, general-purpose processor(s) 1111 and/orDSP(s) 1112 in combination with machine-readable instructions stored onmemory 1140 may compute an estimate of an increment cycle of the sleepcounter at block 510.

Also shown in FIG. 8, a user interface 1135 may comprise any one ofseveral devices such as, for example, a speaker, microphone, displaydevice, vibration device, keyboard, touch screen, just to name a fewexamples. In a particular implementation, user interface 1135 may enablea user to interact with one or more applications hosted on mobile device1100. For example, devices of user interface 1135 may store analog ordigital signals on memory 1140 to be further processed by DSP(s) 1112 orgeneral purpose processor 1111 in response to action from a user.Similarly, applications hosted on mobile device 1100 may store analog ordigital signals on memory 1140 to present an output signal to a user. Inanother implementation, mobile device 1100 may optionally include adedicated audio input/output (I/O) device 1170 comprising, for example,a dedicated speaker, microphone, digital to analog circuitry, analog todigital circuitry, amplifiers and/or gain control. It should beunderstood, however, that this is merely an example of how an audio I/Omay be implemented in a mobile device, and that claimed subject matteris not limited in this respect. In another implementation, mobile device1100 may comprise touch sensors 1162 responsive to touching or pressureon a keyboard or touch screen device.

Mobile device 1100 may also comprise a dedicated camera device 1164 forcapturing still or moving imagery. Camera device 1164 may comprise, forexample an imaging sensor (e.g., charge coupled device or CMOS imager),lens, analog to digital circuitry, frame buffers, just to name a fewexamples. In one implementation, additional processing, conditioning,encoding or compression of signals representing captured images may beperformed at general purpose/application processor 1111 or DSP(s) 1112.Alternatively, a dedicated video processor 1168 may performconditioning, encoding, compression or manipulation of signalsrepresenting captured images. Additionally, video processor 1168 maydecode/decompress stored image data for presentation on a display device(not shown) on mobile device 1100.

Mobile device 1100 may also comprise sensors 1160 coupled to bus 1101which may include, for example, inertial sensors and environment sensorsthat may enable mobile device 1100 to determine relative changes inlocation and/or current speed and heading. Inertial sensors of sensors1160 may comprise, for example accelerometers (e.g., collectivelyresponding to acceleration of mobile device 1100 in three dimensions),one or more gyroscopes or one or more magnetometers (e.g., to supportone or more compass applications). Environment sensors of mobile device1100 may comprise, for example, temperature sensors, barometric pressuresensors, ambient light sensors, camera imagers, microphones, just toname few examples. Sensors 1160 may generate analog or digital signalsthat may be stored in memory 1140 and processed by DPS(s) or generalpurpose application processor 1111 in support of one or moreapplications such as, for example, applications directed to positioningor navigation operations.

In a particular implementation, mobile device 1100 may comprise adedicated modem processor 1166 capable of performing baseband processingof signals received and down converted at wireless transceiver 1121 orSPS receiver 1155. Similarly, modem processor 1166 may perform basebandprocessing of signals to be up converted for transmission by wirelesstransceiver 1121. In alternative implementations, instead of having adedicated modem processor, baseband processing may be performed by ageneral purpose processor or DSP (e.g., general purpose/applicationprocessor 1111 or DSP(s) 1112). It should be understood, however, thatthese are merely examples of structures that may perform basebandprocessing, and that claimed subject matter is not limited in thisrespect.

As depicted, mobile device 1100 may further comprise a sleep countercircuit 1142 that is capable of maintaining a sleep counter by, forexample, incrementing a sleep counter on set increment cycles asdiscussed above. In particular implementations, sleep counter circuit1142 may comprise registers, oscillators, input terminals outputterminals, etc. capable of providing values of a sleep counter. Inparticular embodiments, as discussed above, sleep counter circuit 1142may provide sleep counter values at particular events such as entering asleep state (or other lower power state) and awakening from a sleepstate (or transitioning to other higher power state). In a particularimplementation, for example, sleep counter circuit 1142 may continue toincrement a sleep counter even if mobile device 1100 is in a sleep state(e.g., including removal of power to wireless transceiver 1121, generalpurpose/application processor 1111, DSP(s) 1112, etc.).

FIG. 9 is a schematic diagram illustrating an example system 1200 thatmay include one or more devices configurable to implement techniques orprocesses described above. System 1200 may include, for example, a firstdevice 1202, a second device 1204, and a third device 1206, which may beoperatively coupled together through a wireless communications network1208. First device 1202, second device 1204 and/or third device 1206 maybe used to implement crowdsourcing server 202 and/or location server 206(FIG. 4). In an aspect, first device 1202 may comprise a server capableof providing positioning assistance data such as, for example, a basestation almanac. Also, in an aspect, wireless communications network1208 may comprise one or more wireless access points, for example.However, claimed subject matter is not limited in scope in theserespects.

First device 1202, second device 1204 and third device 1206 may berepresentative of any device, appliance or machine that may beconfigurable to exchange data over wireless communications network 1208.By way of example but not limitation, any of first device 1202, seconddevice 1204, or third device 1206 may include: one or more computingdevices or platforms, such as, e.g., a desktop computer, a laptopcomputer, a workstation, a server device, or the like; one or morepersonal computing or communication devices or appliances, such as,e.g., a personal digital assistant, mobile communication device, or thelike; a computing system or associated service provider capability, suchas, e.g., a database or data storage service provider/system, a networkservice provider/system, an Internet or intranet serviceprovider/system, a portal or search engine service provider/system, awireless communication service provider/system; or any combinationthereof. Any of the first, second, and third devices 1202, 1204, and1206, respectively, may comprise one or more of a base station almanacserver, a base station, or a mobile device in accordance with theexamples described herein. In another example implementation, any of thefirst, second, and third devices 1202, 1204, and 1206, respectively, maycomprise a database to collect, store and update an uncertainty carriernetwork time as maintained at particular base stations in a network foruse as positioning assistance data. Here, for at least one base station,a database may track clock uncertainty. Calibration results may bereceived from one or more mobile devices indicating an uncertainty in aclock maintained at the at least one base station. The tracked clockuncertainty may then be selectively updated with the calibration resultsif the uncertainty indicated by the calibration result is less than athreshold. The updated tracked clock uncertainty may then be increasedover time.

Similarly, wireless communications network 1208 may be representative ofone or more communication links, processes, or resources configurable tosupport the exchange of data between at least two of first device 1202,second device 1204, and third device 1206. By way of example but notlimitation, wireless communications network 1208 may include wireless orwired communication links, telephone or telecommunications systems, databuses or channels, optical fibers, terrestrial or space vehicleresources, local area networks, wide area networks, intranets, theInternet, routers or switches, and the like, or any combination thereof.As illustrated, for example, by the dashed lined box illustrated asbeing partially obscured of third device 1206, there may be additionallike devices operatively coupled to wireless communications network1208.

It is recognized that all or part of the various devices and networksshown in system 1200, and the processes and methods as further describedherein, may be implemented using or otherwise including hardware,firmware, software, or any combination thereof.

Thus, by way of example but not limitation, second device 1204 mayinclude at least one processing unit 1220 that is operatively coupled toa memory 1222 through a bus 1228.

Processing unit 1220 is representative of one or more circuitsconfigurable to perform at least a portion of a data computing procedureor process. By way of example but not limitation, processing unit 1220may include one or more processors, controllers, microprocessors,microcontrollers, application specific integrated circuits, digitalsignal processors, programmable logic devices, field programmable gatearrays, and the like, or any combination thereof.

Memory 1222 is representative of any data storage mechanism. Memory 1222may include, for example, a primary memory 1224 or a secondary memory1226. Primary memory 1224 may include, for example, a random accessmemory, read only memory, etc. While illustrated in this example asbeing separate from processing unit 1220, it should be understood thatall or part of primary memory 1224 may be provided within or otherwiseco-located/coupled with processing unit 1220.

In a particular implementation, processing unit 1220 may executemachine-readable stored in memory 1222 to execute actions and/oroperations at blocks 302, 304, 306 and/or 308 for tracking and updatingan uncertainty in a clock maintained at a base station.

Secondary memory 1226 may include, for example, the same or similar typeof memory as primary memory or one or more data storage devices orsystems, such as, for example, a disk drive, an optical disc drive, atape drive, a solid state memory drive, etc. In certain implementations,secondary memory 1226 may be operatively receptive of, or otherwiseconfigurable to couple to, a computer-readable medium 1240.Computer-readable medium 1240 may include, for example, anynon-transitory medium that can carry or make accessible data, code orinstructions for one or more of the devices in system 1200.Computer-readable medium 1240 may also be referred to as a storagemedium.

Second device 1204 may include, for example, a communication interface1030 that provides for or otherwise supports the operative coupling ofsecond device 1204 to at least wireless communications network 1208. Byway of example but not limitation, communication interface 1230 mayinclude a network interface device or card, a modem, a router, a switch,a transceiver, and the like.

Second device 1204 may include, for example, an input/output device1232. Input/output device 1232 is representative of one or more devicesor features that may be configurable to accept or otherwise introducehuman or machine inputs, or one or more devices or features that may beconfigurable to deliver or otherwise provide for human or machineoutputs. By way of example but not limitation, input/output device 1232may include an operatively configured display, speaker, keyboard, mouse,trackball, touch screen, data port, etc.

The methodologies described herein may be implemented by various meansdepending upon applications according to particular examples. Forexample, such methodologies may be implemented in hardware, firmware,software, or combinations thereof. In a hardware implementation, forexample, a processing unit may be implemented within one or moreapplication specific integrated circuits (“ASICs”), digital signalprocessors (“DSPs”), digital signal processing devices (“DSPDs”),programmable logic devices (“PLDs”), field programmable gate arrays(“FPGAs”), processors, controllers, microcontrollers, microprocessors,electronic devices, other devices units designed to perform thefunctions described herein, or combinations thereof.

Some portions of the detailed description included herein are presentedin terms of algorithms or symbolic representations of operations onbinary digital signals stored within a memory of a specific apparatus orspecial purpose computing device or platform. In the context of thisparticular specification, the term specific apparatus or the likeincludes a general purpose computer once it is programmed to performparticular operations pursuant to instructions from program software.Algorithmic descriptions or symbolic representations are examples oftechniques used by those of ordinary skill in the signal processing orrelated arts to convey the substance of their work to others skilled inthe art. An algorithm is here, and generally, is considered to be aself-consistent sequence of operations or similar signal processingleading to a desired result. In this context, operations or processinginvolve physical manipulation of physical quantities. Typically,although not necessarily, such quantities may take the form ofelectrical or magnetic signals capable of being stored, transferred,combined, compared or otherwise manipulated. It has proven convenient attimes, principally for reasons of common usage, to refer to such signalsas bits, data, values, elements, symbols, characters, terms, numbers,numerals, or the like. It should be understood, however, that all ofthese or similar terms are to be associated with appropriate physicalquantities and are merely convenient labels. Unless specifically statedotherwise, as apparent from the discussion herein, it is appreciatedthat throughout this specification discussions utilizing terms such as“processing,” “computing,” “calculating,” “determining” or the likerefer to actions or processes of a specific apparatus, such as a specialpurpose computer, special purpose computing apparatus or a similarspecial purpose electronic computing device. In the context of thisspecification, therefore, a special purpose computer or a similarspecial purpose electronic computing device is capable of manipulatingor transforming signals, typically represented as physical electronic ormagnetic quantities within memories, registers, or other informationstorage devices, transmission devices, or display devices of the specialpurpose computer or similar special purpose electronic computing device.

Wireless communication techniques described herein may be in connectionwith various wireless communications networks such as a wireless widearea network (“WWAN”), a wireless local area network (“WLAN”), awireless personal area network (WPAN), and so on. The term “network” and“system” may be used interchangeably herein. A WWAN may be a CodeDivision Multiple Access (“CDMA”) network, a Time Division MultipleAccess (“TDMA”) network, a Frequency Division Multiple Access (“FDMA”)network, an Orthogonal Frequency Division Multiple Access (“OFDMA”)network, a Single-Carrier Frequency Division Multiple Access (“SC-FDMA”)network, or any combination of the above networks, and so on. A CDMAnetwork may implement one or more radio access technologies (“RATS”)such as cdma2000, Wideband-CDMA (“W-CDMA”), to name just a few radiotechnologies. Here, cdma2000 may include technologies implementedaccording to IS-95, IS-2000, and IS-856 standards. A TDMA network mayimplement Global System for Mobile Communications (“GSM”), DigitalAdvanced Mobile Phone System (“D-AMPS”), or some other RAT. GSM andW-CDMA are described in documents from a consortium named “3rdGeneration Partnership Project” (“3GPP”). Cdma2000 is described indocuments from a consortium named “3rd Generation Partnership Project 2”(“3GPP2”). 3GPP and 3GPP2 documents are publicly available. 4G Long TermEvolution (“LTE”) communications networks may also be implemented inaccordance with claimed subject matter, in an aspect. A WLAN maycomprise an IEEE 802.11x network, and a WPAN may comprise a Bluetoothnetwork, an IEEE 802.15x, for example. Wireless communicationimplementations described herein may also be used in connection with anycombination of WWAN, WLAN or WPAN.

In another aspect, as previously mentioned, a wireless transmitter oraccess point may comprise a femtocell, utilized to extend cellulartelephone service into a business or home. In such an implementation,one or more mobile devices may communicate with a femtocell via a codedivision multiple access (“CDMA”) cellular communication protocol, forexample, and the femtocell may provide the mobile device access to alarger cellular telecommunication network by way of another broadbandnetwork such as the Internet.

Techniques described herein may be used with an SPS that includes anyone of several GNSS and/or combinations of GNSS. Furthermore, suchtechniques may be used with positioning systems that utilize terrestrialtransmitters acting as “pseudolites”, or a combination of SVs and suchterrestrial transmitters. Terrestrial transmitters may, for example,include ground-based transmitters that broadcast a PN code or otherranging code (e.g., similar to a GPS or CDMA cellular signal). Such atransmitter may be assigned a unique PN code so as to permitidentification by a remote receiver. Terrestrial transmitters may beuseful, for example, to augment an SPS in situations where SPS signalsfrom an orbiting SV might be unavailable, such as in tunnels, mines,buildings, urban canyons or other enclosed areas. Another implementationof pseudolites is known as radio-beacons. The term “SV”, as used herein,is intended to include terrestrial transmitters acting as pseudolites,equivalents of pseudolites, and possibly others. The terms “SPS signals”and/or “SV signals”, as used herein, is intended to include SPS-likesignals from terrestrial transmitters, including terrestrialtransmitters acting as pseudolites or equivalents of pseudolites.

The terms, “and,” and “or” as used herein may include a variety ofmeanings that will depend at least in part upon the context in which itis used. Typically, “or” if used to associate a list, such as A, B or C,is intended to mean A, B, and C, here used in the inclusive sense, aswell as A, B or C, here used in the exclusive sense. Referencethroughout this specification to “one example” or “an example” meansthat a particular feature, structure, or characteristic described inconnection with the example is included in at least one example ofclaimed subject matter. Thus, the appearances of the phrase “in oneexample” or “an example” in various places throughout this specificationare not necessarily all referring to the same example. Furthermore, theparticular features, structures, or characteristics may be combined inone or more examples. Examples described herein may include machines,devices, engines, or apparatuses that operate using digital signals.Such signals may comprise electronic signals, optical signals,electromagnetic signals, or any form of energy that provides informationbetween locations.

While there has been illustrated and described what are presentlyconsidered to be example features, it will be understood by thoseskilled in the art that various other modifications may be made, andequivalents may be substituted, without departing from claimed subjectmatter. Additionally, many modifications may be made to adapt aparticular situation to the teachings of claimed subject matter withoutdeparting from the central concept described herein. Therefore, it isintended that claimed subject matter not be limited to the particularexamples disclosed, but that such claimed subject matter may alsoinclude all aspects falling within the scope of the appended claims, andequivalents thereof.

What is claimed is:
 1. A method, at a mobile device, comprising:obtaining a first value of a sleep counter and a first time stamp inresponse to the mobile device entering a lower power state, wherein thefirst time stamp is referenced to a local network time; entering ahigher power state to acquire a paging signal; obtaining a second valueof the sleep counter and a second time stamp while in the higher powerstate, wherein the second time stamp is referenced to the local networktime; returning to the lower power state; and estimating an incrementcycle of the sleep counter based, at least in part, on a firstdifference between the first time stamp and the second time stamp, andsecond difference between the first value of the sleep counter and thesecond value of the sleep counter.
 2. The method of claim 1, and furthercomprising determining the local network time based, at least in part,on acquisition of the paging signal.
 3. The method of claim 1, andfurther comprising: propagating a system clock time based, at least inpart, on the estimated increment cycle of the sleep counter.
 4. Themethod of claim 3, wherein the system clock time is propagated by anamount based, at least in part, on the second difference multiplied bythe estimated increment cycle of the sleep counter.
 5. The method ofclaim 3, and further comprising initiating acquisition of one or moresatellite positioning system (SPS) signals based, at least in part, onthe propagated system clock time.
 6. The method of claim 5, and furthercomprising determining a time uncertainty for acquisition of the one ormore SPS signals based, at least in part, on a temperature of the mobiledevice.
 7. The method of claim 6, wherein the time uncertainty isfurther determined based, at least in part, on an uncertainty is thelocal network time.
 8. The method of claim 1, and further comprising:receiving a request to perform an SPS position fix while the mobiledevice is in the lower power state; and attempting to perform the SPSposition fix based, at least in part, on the estimated increment cycle.9. The method of claim 1, wherein the lower power state comprises asleep state.
 10. The method of claim 1, wherein the first time stamp andthe second time stamp are obtained during paging slots.
 11. A mobiledevice comprising: a receiver; a sleep counter circuit; and one or moreprocessors configured to: obtain a first value of a sleep counter and afirst time stamp in response to the mobile device entering a lower powerstate, wherein the first time stamp is referenced to a local networktime; transition the mobile device to a higher power state to acquire apaging signal received at the receiver; obtain a second value of thesleep counter and a second time stamp while in the higher power state,wherein the second time stamp is referenced to the local network time;transition the mobile device to the lower power state; and estimate anincrement cycle of the sleep counter based, at least in part, on a firstdifference between the first time stamp and the second time stamp, andsecond difference between the first value of the sleep counter and thesecond value of the sleep counter.
 12. The mobile device of claim 11,wherein the one or more processors are further configured to determinethe local network time based, at least in part, on acquisition thepaging signal.
 13. The mobile device of claim 11, wherein the one ormore processors are further configured to propagate a system clock timebased, at least in part, on the estimated increment cycle of the sleepcounter circuit.
 14. The mobile device of claim 13, wherein the one orprocessors are further configured to propagate the system clock time byan amount based, at least in part, on the second difference multipliedby the estimated increment cycle.
 15. The mobile device of claim 13, andwherein the one or more processors are further configured to initiateacquisition of one or more satellite positioning system (SPS) signalsbased, at least in part, on the propagated system clock time.
 16. Themobile device of claim 15, wherein the one or more processors arefurther configured to determine a time uncertainty for acquisition ofthe one or more SPS signals based, at least in part, on a temperature ofthe mobile device.
 17. A non-transitory storage medium comprisingmachine-readable instructions stored thereon which are executable by oneor more processors of a mobile device to: obtain a first value of asleep counter and a first time stamp in response to the mobile deviceentering a lower power state, wherein the first time stamp is referencedto a local network time; transition the mobile device to a higher powerstate to acquire a paging signal; obtain a second value of the sleepcounter and a second time stamp while in the higher power state, whereinthe second time stamp is referenced to the local network time;transition the mobile device to the lower power state; and estimate anincrement cycle of the sleep counter based, at least in part, on a firstdifference between the first time stamp and the second time stamp, andsecond difference between the first value of the sleep counter and thesecond value of the sleep counter.
 18. The non-transitory storage mediumof claim 17, wherein the machine-readable instructions are furtherexecutable to determine the local network time based, at least in part,on acquisition of the paging signal.
 19. The non-transitory storagemedium of claim 18, wherein the machine-readable instructions arefurther executable to: propagate a system clock time based, at least inpart, on the estimated increment cycle of the sleep counter.
 20. Thenon-transitory storage medium of claim 19, wherein the system clock timeis propagated by an amount based, at least in part, on the seconddifference multiplied by the estimated increment cycle.
 21. Thenon-transitory storage medium of claim 19, wherein the machine-readableinstructions are further executable to initiate acquisition of one ormore satellite positioning system (SPS) signals based, at least in part,on the propagated system clock time.
 22. At a mobile device, anapparatus comprising: means for obtaining a first value of a sleepcounter and a first time stamp in response to the mobile device enteringa lower power state, wherein the first time stamp is referenced to alocal network time; means for entering a higher power state to acquire apaging signal; means for obtaining a second value of the sleep counterand a second time stamp while in the higher power state, wherein thesecond time stamp is referenced to the local network time; means forreturning to the lower power state; and means for estimating anincrement cycle of the sleep counter based, at least in part, on a firstdifference between the first time stamp and the second time stamp, andsecond difference between the first value of the sleep counter and thesecond value of the sleep counter.
 23. The apparatus of claim 22, andfurther comprising means for determining the local network time based,at least in part, on acquisition of the paging signal.
 24. The apparatusof claim 22, and further comprising: means for propagating a systemclock time based, at least in part, on the estimated increment cycle ofthe sleep counter.
 25. The apparatus of claim 24, wherein the systemclock time is propagated by an amount based, at least in part, on thesecond difference multiplied by the estimated increment cycle of thesleep counter.
 26. The apparatus of claim 24, and further comprisingmeans for initiating acquisition of one or more satellite positioningsystem (SPS) signals based, at least in part, on the propagated systemclock time.
 27. The apparatus of claim 26, and further comprising meansfor determining a time uncertainty for acquisition of the one or moreSPS signals based, at least in part, on a temperature of the mobiledevice.
 28. The apparatus of claim 27, wherein the time uncertainty isfurther determined based, at least in part, on an uncertainty is thelocal network time.